The availability of clean water has emerged as one of the most serious problems facing the global economy in the 21st century. See Savage, N. and Diallo, M. S. (2005) “Nanomaterials and Water Purification,” Journal of Nanoparticle Research, 7(4-5): 331-42. Anions such as bromide, nitrate, and sulfate are major targets in water and wastewater treatment. Bromide (Br−) is commonly found in surface water and groundwater. It can become a contaminant in drinking water when it is oxidized with ozone to bromate (BrO3−) during primary disinfection. The United States Environmental Protection Agency (USEPA) has identified bromate as a potential carcinogen and has established a maximum contaminant limit (MCL) of 0.01 mg/L in potable water. See 40 CFR 141.64(a). Because ozone does not generate a residual taste, color and odor in water, the multi-billion dollar U.S. bottled water industry uses ozonation to disinfect water prior to bottling and shipping. Removal of bromide from drinking water sources prior to ozonation is considered to be an effective means of satisfying the bromate MCL requirement.
Reverse osmosis (RO) is currently being used as the primary treatment process to remove bromide from water sources at most bottled water treatment plants. However, it is expensive to implement due the high pressure (e.g., roughly 10-70 bar) required to operate RO membranes. See American Water Works Association, Reverse Osmosis and Nanofiltration (M46), 2d ed., Denver, 2007. Moreover, two to three RO passes are often required to reduce bromide to acceptable levels prior to ozonation because of the limited bromide rejection capability of current RO membranes. Ion exchange (IX) is a widely used process for removing anions from water. See Gu, B. and Brown, G. M. (2006) “Recent advances in ion exchange for perchlorate, treatment, recovery and destruction,” in Perchlorate Environmental Occurrence, Interactions and Treatment, Gu, B. and Coates, J. D., eds., Springer: New York, pp. 209-51. However, major drawbacks of IX include limited binding capacity/selectivity for bromide, and environmental impact (e.g., brine management and disposal). See id. Because of this, the bottled water industry is in critical needed for efficient, cost effective and environmentally acceptable technologies for removing bromide from drinking water sources prior to ozonation.
Nitrate (NO3−) is one of the most ubiquitous contaminants in groundwater, surface water and wastewater. It can reduce the ability of red blood cells to carry oxygen when ingested. The MCL of nitrate in drinking water is 45 mg/L. See Shannon, M. A., Bohn, P. W., Elimelech, M, et al. (2008), “Science and technology for water purification in the coming decades,” Nature, 54: 301-10. Nitrate is often found in agricultural run-offs and municipal wastewater. The discharge of wastewater with excess nitrate in the Mississippi River has emerged as one of the main cause of hypoxia (i.e. oxygen deficiency) and the formation of the yearly “Dead Zone” in the Northern Gulf of Mexico (e.g., Louisiana and Texas). Nitrate removal from wastewater is a billion dollar industry in the US.
Biological processes (e.g., fluidized bed bioreactors, biological filters and membrane bioreactors) can effectively reduce nitrate to nitrogen (N2) under anaerobic conditions. See Cheremisinoff, N. P. (2002) Handbook of Water and Wastewater Treatment Technologies, Butterworth-Heinemann: Boston. However, they are very sensitive to temperature changes. For example, a 10° C. decrease in temperature can cause up to a 50% reduction in biological denitrification activity. See Reynolds, T. D. & Richards, P. A. (1996) Unit Operations and processes in Environmental Engineering, 2d ed., PWS Publishing: Boston. Because of this, most wastewater treatment plants in the US cannot meet their nitrate discharge limit during the winter.
Excess sulfate is also considered harmful in drinking water. It may cause diarrhea in adults and infants when exposed suddenly to high levels of sulfate. (See Chien, L et al. (1968), “Infantile gastroenteritis due to water with high sulfate content,” Can Med Assoc J. 99:102-104.
One approach to removing various contaminants from water is to use water-soluble branched macromolecules that selectively encapsulate dissolved solutes in aqueous solutions followed by ultrafiltration. See, e.g., U.S. Patent App. No. 2006/0021938 A1 (published Feb. 2, 2006); U.S. patent application Ser. No. 12/124,952; Diallo, M. S., Chritie, S., Swaminathan, P., Johnson, J. H. Jr., and Goddard W. A. III (2005) “Dendrimer Enhanced Ultrafiltration. 1. Recovery of Cu(II) from Aqueous Solutions Using Gx-NH2 PAMAM Dendrimers with Ethylene Diamine Core,” Environmental Science and Technology, 39(5): 1366-77; Diallo, M. S., Chritie, S., Swaminathan, P., Balogh, L., Shi, X., Um, W., Papelis, L, Goddard, W. A. III, and Johnson, J. H. Jr. (2004) “Dendritic Chelating Agents 1. Cu(II) Binding to Ethylene Diamine Core Poly(amidoamine) Dendrimers in Aqueous Solutions,” Langmuir 20(7): 2640-51; Diallo, M. S., Wondwossen, A., Johnson, J. H. Jr., and Goddard, W. A. III (2008) “Dendritic Chelating Agents 2. U(VI) Binding to Poly(amidoamine) and Poly(propyleneimine) Dendrimers in Aqueous Solutions,” Environmental Science and Technology, 42: 1572-79; and Diallo, M. S., Falconer, K., Johnson, J. H. Jr. and Goddard, W. A. Jr. (2007) “Dendritic Anion Hosts: Perchlorate Binding to G5-NH2 Poly(propyleneimine) Dendrimer in Aqueous Solutions,” Environmental Science and Technology, 41: 6521-27. See also U.S. Patent App. No. 2010/0181257 A1 (published Jul. 22, 2010), which is incorporated herein in its entirety.
There is a need, however, to develop effective novel macromolecules that enable anions such as bromide, nitrate, and sulfate removal technologies that are efficient, cost effective, and readily implemented using existing water or wastewater treatment equipment and infrastructure.